1. Field of the Invention
The invention relates to box beam style guardrail installations and safety end treatments for such installations. The invention also relates to methods of use associated with these devices.
2. Description of the Related Art
Guardrail installations are used along roadways to prevent errant vehicles from leaving a roadway wherein they may encounter hazards that are a substantial danger to them. In its simplest form, the guardrail installation features a horizontally disposed rail member that is supported above the ground by a series of support posts. The rail member is most commonly provided by longitudinal segments of corrugated sheet steel having a W-shaped cross-section. Other corrugated rail members, such as the “thrie-beam” are used in some situations. Alternative guardrail installation designs, and those that this patent is concerned with, incorporate a box beam rail member wherein the rail member is a tubular beam member having a square or rectangular cross-section. Box beam terminals are popular in some northern tier markets, including New York and Wyoming, primarily because the use of box beams permits wider support post spacing and greater ground clearance and, hence, reduces snow drift problems in winter time.
A guardrail installation should be installed along a roadside or median such that its ends do not in themselves form a hazard. Early guardrail installations lacked any safety termination at the upstream ends, and occasionally, impacting vehicles became impaled on the ends causing intense deceleration of the vehicle and severe injury to the occupants. In some reported cases, the guardrail end penetrated into the occupant compartment of the vehicle with fatal results.
Upon recognition of the need for proper upstream guardrail termination, guardrail installation designs were developed to reduce the hazard associated with the end of the guardrail. One commonly used technique was to “turn down” the end of the guardrail and bury it into the ground. This method has some recognized disadvantages, including an unintended possibility of ramping an approaching vehicle off the ground during a collision, which can result in a violent vehicular rollover.
A number of end treatments have also been developed for use with corrugated rail members. Perhaps the most popular of these end treatments is the Guardrail Extruder Terminal, described in U.S. Pat. Nos. 4,928,928 and 5,078,366, which have been assigned to the assignee of the present invention and are incorporated herein by reference. Guardrail Extruder Terminal end treatments are known commercially as “ET-2000.” Other end treatments are known as well that are useful for corrugated rail-style guardrail installations.
Box beam guardrail installations have significantly different, and fewer, end treatments as compared with corrugated rail guardrail installations. This is, in part, because the beam members have a hollow cross section and have a much larger axial buckling load and a much larger lateral bending resistance than the corrugated rail. The tubular nature of the box beam tends to suggest the use of telescoping segments in a collapsing mechanism. One type of box beam guardrail termination is described in U.S. Pat. No. 5,391,016 issued to Ivey et al. and assigned to the assignee of the present invention. In this arrangement, the upstream end of the guardrail installation is provided with nested, telescoping rail segments. The segments are compressed by telescoping inwardly upon one another during an end-on collision. Resistance to the telescoping action is provided by a filler material (i.e., fiberglass) that is mechanically crushed during the compression process. This style of box beam guardrail termination is highly effective. However, proper filler material may be costly and/or difficult to obtain in some areas. Further, long, slender telescoping tubes, such as those used in some prior art systems, can have stability problems when impacted in an eccentric manner. Such stability problems can restrict the telescoping behavior. Such crushable composite tubes are also subject to manufacturing variability, which can influence the magnitude of the crush force. The decelerations resulting from the staged composite tube design are sensitive to vehicle mass and impact speed.
The present invention addresses the problems of the prior art.